1.1 Atomism from Democritus to Feynman
Science in the Western culture goes back to Ancient Greece, namely the Presocratic natural philosophers. Among them are Leucippus and Democritus (about 400 B.C.), who were the first atomists. Democritus is reported as maintaining that
In a similar vein, Isaac Newton writes at the end of the Opticks:ā¦ substances infinite in number and indestructible, and moreover without action or affection, travel scattered about in the void. When they encounter each other, collide, or become entangled, collections of them appear as water or fire, plant or man. (Fragment Diels-Kranz 68 A57; quoted from Graham 2010, p. 537)
To turn to contemporary physics, Richard Feynman says at the beginning of the famous Feynman lectures:ā¦ it seems probable to me, that God in the Beginning formād Matter in solid, massy, hard, impenetrable, moveable Particles ā¦ the Changes of corporeal Things are to be placed only in the various Separations and new Associations and motions of these permanent Particles. (Quoted from Newton 1952, question 31, p. 400)
This is atomism. The success story of modern science is at its roots the success story of atomism. It is evident from these quotations why atomism is attractive: on the one hand, it is a proposal for a theory about what there is in the universe that is both most parsimonious and most general. On the other hand, it offers a clear and simple explanation of the realm of the objects that are accessible to us in perception. Any such object is composed of a large number of discrete, pointlike particles. All the differences between these objectsāat a time as well as in timeāare accounted for in terms of the spatial configuration of these particles and its change. This view is implemented in classical mechanics. It conquered the whole of physics via classical statistical mechanics (e.g. heat as molecular motion), chemistry via the periodic table of elements, biology via molecular biology (e.g. molecular composition of the DNA), and finally neuroscienceāneurons are composed of particles, and neuroscience is applied physics. In a nutshell, what paved the way for the success of science is the idea to decompose everything into elementary particles and to explain it on the basis of the interactions of these particles.If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atomsālittle particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied. (Feynman et al. 1963, ch. 1ā2)
To understand how the atoms interact, one needs laws that describe their motion. That is why atomism remains a speculative stance in Antiquity and becomes science only in modern times: only modern physics formulates laws of motion for the atoms. Nonetheless, the attractiveness of atomism does not depend on what precisely is proposed as these laws. Its attractiveness is independent of a particular physical theory. It consists in the idea of composition by particles together with the idea that differences in this composition account for all the differences that there are. There is a direct and intuitive link from this idea to the observable, macroscopic objects.
That link is direct and intuitive because all that is observed in science as well as in common sense are the positions of discrete objects relative to each other and the change of these positionsāin other words, the variation in the distances among discrete objects that make up a configuration of objects and the change of such configurations. Accordingly, all measurement outcomes are recorded as relative positions within configurations of discrete objects and variations of such positions, such as, for instance, pointer positions or digital numbers on a screen. In this vein John Bell (2004, p. 166) famously says āā¦ in physics the only observations we must consider are position observations, if only the positions of instrument pointersā. The qualification āin physicsā is appropriate, because common sense observations typically involve colours, sounds or scents of spatially arranged objects. The positions of objects are discerned by means of these sensory qualities. However, sensory qualities do not figure in physical theories, at least not explicitly (we will consider that issue in Sect. 3.ā1).
That notwithstanding, all the evidence that we have in science is evidence of positions of discrete objects relative to other discrete objects. For instance, even in the case of the gravitational waves detected by LIGO (Laser Interferometer Gravitational-Wave Observatory) in 2016, all the evidence is evidence of change in the relative positions of discrete objects that finally are particles. This change then is mathematically described in terms of a wave rippling through the gravitational field. This fact highlights again the direct link between the experimental evidence and the idea of atomism: it is relative positions of discrete objects all the way down from the macroscopic objects to their ultimate constituents, or all the way up from the ultimate constituents to the macroscopic objects. Thus, if a theory gets the spatio-temporal arrangement of the particles right (that is, the arrangement of fermionic matter according to contemporary physics),1 it has got everything right that can ever be checked in scientific experiments.2 Two theories that agree on the spatio-temporal arrangement of the particles cannot be distinguished by any empirical means, whatever else they may otherwise say and disagree on. By the same token, two possible worlds with the same spatio-temporal arrangement of the particles are indiscernible by any scientific means.
Hence, what is relevant for the account of the perceptible macroscopic objects and their differences are only the relative positions of the particlesāin other words, how far apart they are from each other, that is, their distancesāand the change of these distances. Any intrinsic nature of the atoms is irrelevant for that task. Realizing this point stands in contrast to the mainstream tradition in ancient and medieval thought where the focus was on an inner form (eidos) of the objectsāthat is, some characteristic, intrinsic features that belong to each object considered independently of all the other objects. Aristotleās Categories and Metaphysics are the locus classicus of this tradition. To put it differently, on atomism, the atoms are the substance of the world. They are permanent: they do not come into existence and they do not go out of existence. But they are substances only in the sense of permanent existence. They are not substances in the sense of having an inner form. The atoms are featureless. All there is to them are their positions relative to each otherāthat is, their distancesāand the change of these positions.
RenĆ© Descartes is the central figure who brought about the shift from Aristotelian forms in the medieval, scholastic conception of nature to an essence of the material objects that consists only in their extensionāthat is, the spatial relations or distances among these objectsāand motion (that is, the change of these spatial relations). In short, for Descartes, nature is only res extensa . Descartes also formulated laws of motion. But these did by and large not turn out to be correct, mainly because Descartes conceived the interaction of the material objects in a mechanical way as direct contact. Laws of interaction that prevailed go back to Newton, with the law of gravitation being the prime example. Newtonian gravitation is interaction without direct contact, as in the attraction of the Earth by the Sun. Let us therefore have a closer look at the interplay between objects and laws.
1.2 Primitive Ontology
The atoms that atomism poses cannot be further decomposed into smaller things, because they are not extended themselves: they are point particles. All the extension comes from the spatial relations in which they stand, making up for configurations of point particles. These are the bedrock of the universe so to speak, since one cannot go further down than spatially arranged point particles in scientific enquiry. In other words, their configurations are the ultimate referents of our scientific theories, what they talk about in the last resort. Let us introduce the philosophical term primitive ontology. Ontology is about what there is (to on in ancient Greek). The primitive ontology is about what is admitted as simply existing in the sense that it cannot be derived from anything else or introduced in terms of its function for anything else. What takes this place depends on our theories: it is the hypothesis of science that the universe is ultimately constituted by spatially arranged point particles. If this hypothesis is right, then the particle configuration of the universe is the bedrock, at least as far as scientific enquiry is concerned.
Are there alternatives to atomism? The Presocratic natural philosophers do not only include the atomists Leucippus and Democritus. Before them came Thales, Anaximander, Anaximenes and Anaxagoras who searched for the stuff out of which everything is made. Thales apparently took water to be that stuff, whereas the others thought of it as something more abstract. In any case, the stuff view of nature is opposed to atomism: instead of a plurality of discrete, indivisible objects, there is just one continuous stuff that stretches out throughout the universe. One problem with this view is that one may find the idea of a bare stuff substratum of matter mysterious. Furthermore, that stuff substratum admits of different degrees of density as a primitive matter of fact: there is more stuff in some regions of space than in others. In brief, there is nothing in this view that individuates o...